Bolometer is a device sensitive to thermal radiation and can convert invisible radiation into visible or measurable signals. By refrigerating method, bolometers may be classified into refrigerating bolometers and non-refrigerating bolometers. As non-refrigerating bolometers have such advantages as working at room temperature, no need of refrigeration, spectral response independent of wavelength, a relatively simple preparation process, low cost, small volume, easy use and maintenance and high reliability and/or the like, they have become a very promising development direction of bolometers.
Currently, the most popular non-refrigerating bolometer is vanadium oxide microbridge bolometer. It realizes thermal detection by a vanadium oxide thermosensitive film with a high temperature coefficient of resistance (TCR) on the surface of the microbridge. The preparation process of this type of bolometer includes four parts (refer to FIG. 1): (1) preparing a readout integrated circuit (ROIC) of an thermal radiation detector on a silicon wafer; (2) depositing a thin-film sacrificial layer and lithography and etching; (3) depositing a low-stress silicon nitride supporting layer and a vanadium oxide film on the patterned sacrificial layer, preparing a metal layer for interconnection, and lastly depositing a very thin silicon nitride protective layer on the surface of the film; (4) etching the sacrificial layer on the silicon wafer and releasing the microbridge of the thermal radiation detector.
In the process flow shown in FIG. 1, after the ROIC is prepared, an appropriate chemical-mechanical polishing (CMP) process is needed to realize flattening of silicon wafer surface to control the subsequent uniformity of surface height of the microbridge structure. Therefore, this process flow needs to use a strict ROIC flattening technique. In addition, the foregoing structure needs to reserve an enough space for the export of electrical signals on the edge of the microbridge, so it is adverse to the downsizing of the entire detection unit. Furthermore, this structure is prepared on a same substrate and has strict requirements for process integration and process control.